Proof of Saint-Marceaux's taste for Italy, Spirit Guarding the Secret of the Tomb was executed after his second stay in Italy in the early 1870s. The artist deeply admired the Florentine Renaissance and Michelangelo in particular. His Spirit is thus directly inspired by the male figures in the Sistine Chapel. The body is hunched and yet twisted in a way that recalls the compositions of the great Renaissance sculptor. With remarkably simple lines and movement, Saint-Marceaux has arranged the limbs so as to obtain a rotating movement. The figure is rolled around a funerary urn in a defiant attitude. Contrasting with the nude body, the veil stirred by the wind punctuates the volumes with areas of shade.

Such mastery of composition, powerful expression and broad design earned the sculptor the medal of honour in 1879. The image was made popular by engraving, to the extent that during the Dreyfus affair it was used to denounce the anti-Semitic officer who had falsified the document behind the captain's condemnation. In a caricature entitled "Colonel Henry Guarding the Secret of the General Staff", we see a soldier in a posture similar to that of Saint-Marceaux's Spirit jealously guarding the urn containing the false evidence fabricated by the army.